This invention relates to a bubble collection type gas electrode which is dipped in an electrolyte and collects bubbles of a reaction gas which are introduced into the electrolyte.
Conventionally, as shown in FIG. 1, a gas diffusion electrode has been composed of a reaction layer (a) which is prepared by impregnating a porous member composed of, for example, hydrophilic carbon black and PTFE (polytetrafluoroethylene) with a catalyst such as platinum, and a gas supply layer (b) composed of hydrophobic carbon black and PTFE bonded together by means of a nickel mesh current collector (c). This kind of gas diffusion electrode cannot collect bubbles so the idea to employ the gas diffusion electrode dipped in an electrolyte has not existed. A pair of the gas diffusion electrodes may be dipped in an electrolyte in an electrolytic cell and opposed to each other where a diaphragm (for example, a cation exchange membrane) is disposed therebetween. This gas diffusion electrode collects mixed bubbles such as hydrogen and oxygen in the electrolyte on the surface of the hydrophobic gas supply layer and supplies the collected gas as a reaction gas to the reaction layer for effecting an electrode reaction.
In this conventional gas diffusion electrode, however, the surface of the gas diffusion layer (b) possesses hydrophobicity so that a bubble (B) adhered to the surface of the gas diffusion layer (b) is pushed toward the surface due to the water pressure as shown in FIG. 1 and rapidly moves upward along the surface as shown in FIG. 2 to produce a drawback that the bubble only insufficiently stays on the electrode surface.
In order to increase the hydrophobicity of the surface of the gas supply layer, it may be coated with a porous PTFE film. Because of the hydrophobicity and the smoothness of the PTFE film, it is difficult for the reaction gas bubbles to adhere on the surface of the film so that the gas supply rate to the reaction layer through the gas diffusion layer is low, the electrode reaction is insufficient; and the electrolysis efficiency is low. Accordingly, the reaction cannot be effected in a high current density. Further, the hydrophobicity of the surface of the gas diffusion layer may be promptly lowered and easily wetted to make its life shorter due to the decrease of the gas supplying ability.
Due to these drawbacks, the conventional gas diffusion electrode has not been used when electrodes are to be dipped in the electrolyte.